CuWO4 and Co3O4 composite material as well as preparation method and application thereof

Abstract

The invention discloses a CuWO4-coated Co3O4 composite material as well as a preparation method and application thereof, and relates to the technical field of chemical catalytic materials. The method comprises the following steps: dropwise adding a NaWO4. 2H2O solution into a Cu (NO3) 2.3 H2O solution, and carrying out a reaction to prepare CuWO4 nanoparticles; the preparation method comprises the following steps: sequentially adding a CoCl2. 6H2O solution and a NaOH solution into a Co (NO3) 2.6 H2O solution, and reacting to prepare a Co3O4 nanocube; and mixing and dispersing in ethanol to prepare the CuWO4 and Co3O4 composite material. The composite material prepared by the invention has high photoelectrocatalysis performance, and has high synthetic ammonia yield, Faraday efficiency and chemical stability. According to the invention, the problem of low ammonia synthesis efficiency caused by serious recombination of photogenerated charge carriers, slow charge migration and insufficient light absorption of the existing photoelectric catalyst is solved.

Description

Technical Field

[0001] This invention relates to the field of chemical catalytic materials technology, specifically to a CuWO4@Co3O4 composite material, its preparation method, and its application. Background Technology

[0002] Ammonia (NH3) is an important basic chemical widely used in agriculture, industry, and energy storage. Currently, ammonia is mainly synthesized from nitrogen (N2) and hydrogen (H2) under high temperature and pressure via the Haber-Bosch process. Developing ammonia production processes that can operate under conventional environmental conditions and are driven by renewable energy has become a hot research topic. Photoelectrocatalytic ammonia synthesis, as a clean and low-carbon disruptive technology, has the potential to utilize solar energy to drive the hydrogenation reaction of nitrogen and water at ambient temperature and pressure, enabling the synthesis of green ammonia under mild conditions. However, the efficiency of photoelectrocatalytic ammonia synthesis remains low, with yields far from industrial-scale levels (<2 mmol·g). -1 ·h -1 The reason for this is the high activation barrier of the N≡N bond (941 kJmol⁻¹) and the low solubility of nitrogen (0.66 mmol L⁻¹), which makes the Faraday efficiency of photoelectrocatalytic nitrogen reduction much lower than that of the Haber-Bosch process. Therefore, improving the activation efficiency of nitrogen molecules and overcoming the low solubility and high-energy barriers in traditional photoelectrocatalytic nitrogen reduction reactions (PE-NRR) has become a key challenge for this technology. In recent years, nonthermal plasma technology has become a highly regarded alternative method due to its ability to efficiently activate nitrogen at room temperature and pressure. Nonthermal plasma can directly activate the N≡N bond through high-energy electron collisions with N2 molecules, and oxidize them to generate more reactive NO and NO2. Subsequently, these NO... x (x=1, 2) will be collected in the absorbent solution and converted into nitrite (NO2). ⁻ ) and nitrates (NO3) ⁻ NO is used as an electrolyte in subsequent photoelectrocatalytic ammonia synthesis reactions. Compared to the high activation energy of traditional N≡N bonds, NO... x ⁻ The N=O bond has a low activation energy (204 kJ mol⁻¹), which makes it suitable for photoelectrocatalysis of NO. x ⁻ Reduction reaction (PE-NO) x - The reduction reaction (RR) is more likely to occur than the reduction reaction of N2. In addition, plasma ammonia synthesis does not rely on energy-intensive H2 and can directly use water vapor or moisture in the air as a hydrogen source, thereby further reducing the carbon footprint.

[0003] Although nitrogen gas, which has high dissociation properties, is converted into more reactive NO through low-temperature plasma, x⁻ , can significantly improve the efficiency of ammonia synthesis. However, there are few reports on the coupling of plasma activated nitrogen and photoelectrocatalytic synthesis of ammonia, and the NH3 yield is relatively low. The main reason is that the practical application of most photocatalysts is hindered by low solar energy conversion efficiency. Due to the serious recombination of photo-generated charge carriers, slow charge transfer and insufficient light absorption, the photoelectrocatalytic NO x ⁻ Reduction reaction (PE-NO x - RR) reaction kinetics is slow. At the same time, NO3 ⁻ The eight-electron reduction path has a high-energy barrier intermediate step, and the competitive HER causes the loss of faradic efficiency. Therefore, preparing a composite material with multiple recombination sites, high photocatalytic performance and conductivity, high selectivity and photoelectrocatalytic efficiency is one of the key problems to be solved in the field of plasma coupled photoelectrocatalytic synthesis of ammonia at present. SUMMARY

[0004] In order to solve the above technical problems, the purpose of the present application is to provide a CuWO4@Co3O4 composite material and its preparation method and application, in order to solve the problem of low efficiency of ammonia synthesis caused by serious recombination of photo-generated charge carriers, slow charge transfer and insufficient light absorption of existing photoelectrocatalysts.

[0005] The technical scheme for solving the above technical problems is as follows: a preparation method of CuWO4@Co3O4 composite material is provided, comprising the following steps: (1) NaWO4·2H2O solution is added dropwise into Cu(NO3)2·3H2O solution, stirred, then reacted, cooled to room temperature, and then separated and calcined to prepare CuWO4 nanoparticles; (2) CoCl2·6H2O solution and NaOH solution are added into Co(NO3)2·6H2O solution in sequence, stirred, then reacted, cooled to room temperature, and then separated, dried and calcined to prepare Co3O4 nanocubes; (3) The CuWO4 nanoparticles prepared in step (1) and the Co3O4 nanocubes prepared in step (2) are mixed, dispersed in ethanol, ultrasonicated, then stirred, and then calcined to prepare CuWO4@Co3O4 composite material.

[0006] On the basis of the above technical scheme, the present application can also be improved as follows: Further, in step (1), the volume ratio of NaWO4·2H2O solution to Cu(NO3)2·3H2O solution is 0.8-1.2:0.8-1.2.

[0007] Further, in step (1), the volume ratio of the NaWO4.2H2O solution and the Cu(NO3)2.3H2O solution is 1:1.

[0008] Further, in step (1), the mass volume ratio of NaWO4.2H2O and solvent in the NaWO4.2H2O solution is 0.25-0.35 g: 15 mL, and the solvent is deionized water.

[0009] Further, in step (1), the mass volume ratio of NaWO4.2H2O and solvent in the NaWO4.2H2O solution is 0.2938 g: 15 mL, and the solvent is deionized water.

[0010] Further, in step (1), the mass volume ratio of Cu(NO3)2.3H2O and solvent in the Cu(NO3)2.3H2O solution is 0.2-0.3 g: 15 mL, and the solvent is deionized water.

[0011] Further, in step (1), the mass volume ratio of Cu(NO3)2.3H2O and solvent in the Cu(NO3)2.3H2O solution is 0.2416 g: 15 mL, and the solvent is deionized water.

[0012] Further, in step (1), stirring is performed for 20-40 min.

[0013] Further, in step (1), stirring is performed for 30 min.

[0014] Further, in step (1), the reaction is performed at 150-200°C for 20-30 h.

[0015] Further, in step (1), the reaction is performed at 180°C for 20-30 h.

[0016] Further, in step (1), a hydrothermal reaction is performed.

[0017] Further, in step (1), the precipitate is obtained by centrifugation, and then the separation process is completed by washing with deionized water and ethanol in sequence.

[0018] Further, in step (1), calcination is performed at 400-600°C for 1-3 h.

[0019] Further, in step (1), calcination is performed at 500°C for 2 h.

[0020] Further, the temperature is raised to 400-600°C at a temperature raising rate of 4-6°C.

[0021] Further, the temperature is raised to 500°C at a temperature raising rate of 5°C.

[0022] Further, in step (2), the volume ratio of CoCl2.6H2O solution, NaOH solution and Co(NO3)2.6H2O solution is 7-8:7-8:12-18.

[0023] Further, in step (2), the volume ratio of CoCl2.6H2O solution, NaOH solution and Co(NO3)2.6H2O solution is 7.5:7.5:15.

[0024] Further, in step (2), the mass-volume ratio of CoCl2.6H2O and solvent in CoCl2.6H2O solution is 1-2g:7-8mL, and the solvent is water.

[0025] Further, in step (2), the mass-volume ratio of CoCl2.6H2O and solvent in CoCl2.6H2O solution is 1.7845g:7.5mL, and the solvent is water.

[0026] Further, in step (2), the mass-volume ratio of NaOH and solvent in NaOH solution is 0.2-0.5g:7-8mL, and the solvent is water.

[0027] Further, in step (2), the mass-volume ratio of NaOH and solvent in NaOH solution is 0.3g:7.5mL, and the solvent is water.

[0028] Further, in step (2), the mass-volume ratio of Co(NO3)2.6H2O and solvent in Co(NO3)2.6H2O solution is 4-5g:12-18mL, and the solvent is water.

[0029] Further, in step (2), the mass-volume ratio of Co(NO3)2.6H2O and solvent in Co(NO3)2.6H2O solution is 4.3655g:15mL, and the solvent is water.

[0030] Further, in step (2), stirring is performed for 20-40min.

[0031] Further, in step (2), stirring is performed for 30min.

[0032] Further, in step (2), the reaction is performed at 150-200℃ for 5-10h.

[0033] Further, in step (2), the reaction is performed at 180℃ for 5h.

[0034] Further, in step (2), hydrothermal reaction is performed.

[0035] Further, in step (2), the precipitate is obtained by centrifugation, and then the separation process is completed by washing with deionized water.

[0036] Further, in step (2), vacuum drying is performed at 50-70 DEG C for 5-10 h.

[0037] Further, in step (2), vacuum drying is performed at 60 DEG C for 8 h.

[0038] Further, in step (2), calcination is performed at 300-400 DEG C for 1-3 h.

[0039] Further, in step (2), calcination is performed at 350 DEG C for 2 h.

[0040] Further, the temperature is raised to 300-400 DEG C at a temperature raising rate of 2-4 DEG C.

[0041] Further, the temperature is raised to 350 DEG C at a temperature raising rate of 3 DEG C.

[0042] Further, in step (3), the molar volume ratio of Cu atoms in CuWO4 nanoparticles, Co atoms in Co3O4 nanocubes and ethanol is 1 mol:0.1-1 mol:30 mL.

[0043] Further, in step (3), the molar volume ratio of Cu atoms in CuWO4 nanoparticles, Co atoms in Co3O4 nanocubes and ethanol is 1 mol:0.7 mol:30 mL.

[0044] Further, in step (3), stirring is performed at 40-80 DEG C.

[0045] Further, in step (3), stirring is performed at 60 DEG C.

[0046] Further, in step (3), stirring is performed until ethanol is completely evaporated.

[0047] Further, in step (3), calcination is performed at 150-200 DEG C for 1-3 h.

[0048] Further, in step (3), calcination is performed at 180 DEG C for 2 h.

[0049] Further, the temperature is raised to 150-200 DEG C at a temperature raising rate of 4-6 DEG C.

[0050] Further, the temperature is raised to 180 DEG C at a temperature raising rate of 5 DEG C.

[0051] The application further provides a CuWO4@Co3O4 composite material prepared by the above method.

[0052] The application further provides application of the above CuWO4@Co3O4 composite material in plasma-coupled photoelectrocatalytic synthesis of ammonia.

[0053] The application has the following beneficial effects: 1、CuWO4@Co3O4 composite material heterojunction prepared by the application reduces the valence band position of CuWO4@Co3O4-x, reduces the free energy of the electron transition from CuWO4 to Co3O4, is conducive to accelerating the transfer of electrons, and further promotes the synthesis of ammonia. x - The reduction reaction CuWO4@Co3O4-x has a strong NO x - adsorption effect, which provides a good foundation for the activation of the subsequent N=O double bond and the subsequent hydrogenation reduction step of the intermediate; at the same time, the construction of the heterojunction reduces the recombination of photo-generated electrons and holes, accelerates the charge transfer, and significantly improves the photoelectrocatalytic synthesis of ammonia effect.

[0054] 2、The CuWO4@Co3O4 composite material provided by the application can be used for plasma-coupled tube photoelectrocatalytic synthesis of ammonia, so that the ammonia synthesis yield can reach 267.2 mmol·h -1 ·g cat -1 and 85 % or so Faraday efficiency, and the ammonia production efficiency almost does not decrease after 6 cycles of testing, and has good chemical stability.

[0055] 3、The composite material prepared by the application has high photoelectrocatalytic performance, high ammonia synthesis yield, Faraday efficiency and chemical stability. BRIEF DESCRIPTION OF DRAWINGS

[0056] Figure 1 XRD pattern of the composite material prepared in Example 4; Figure 2 UV-Vis diffuse reflection spectrum of CuWO4, Co3O4 of Example 4 and composite materials of Examples 1-5; Figure 3 UV-Vis diffuse reflection band gap diagram of CuWO4, Co3O4 and composite material of Example 4; Figure 4 Nitrogen adsorption-desorption isotherm and pore size distribution diagram of CuWO4 of Example 4; Figure 5 Nitrogen adsorption-desorption isotherm and pore size distribution diagram of Co3O4 of Example 4; Figure 6 Nitrogen adsorption-desorption isotherm and pore size distribution diagram of the composite material prepared in Example 4; Figure 7 Linear sweep voltammetry curve diagram of CuWO4, Co3O4 and composite material of Example 4; Figure 8Transient photocurrent plots for CuWO4, Co3O4 and composite materials of Example 4; Figure 9 Electrochemical impedance plots for CuWO4, Co3O4 and composite materials of Example 4; Figure 10 Electrochemical ammonia synthesis efficiency and Faradaic efficiency plots for CuWO4, Co3O4 and composite materials of Examples 1-5 of Example 4; Figure 11 Cycling stability test results plots for composite materials prepared in Example 4. DETAILED DESCRIPTION

[0057] The principles and features of the present application are described below in conjunction with the accompanying drawings, in which the examples are used to explain the present application and are not intended to limit the scope of the present application. The specific conditions are not specified in the examples, and the conventional conditions or the conditions recommended by the manufacturer are used. The reagents or instruments used are not specified by the manufacturer, and are conventional products that can be purchased on the market.

[0058] Example 1: A CuWO4@Co3O4 composite material, the preparation method comprising the following steps: (1) A NaWO4·2H2O solution (solute 0.2938 g, deionized water 15 mL) was added dropwise into a Cu(NO3)2·3H2O solution (solute 0.2416 g, deionized water 15 mL), continuously stirred at room temperature for 30 min, then transferred to a 50 mL polytetrafluoroethylene lined reaction kettle, and hydrothermally reacted at 180°C for 24 h, naturally cooled to room temperature, then centrifuged at 8000 rpm to obtain a precipitate, which was washed with deionized water and ethanol in sequence to remove impurities, placed in a muffle furnace, heated to 500°C at a heating rate of 5°C, and calcined for 2 h to obtain CuWO4 nanoparticles; (2) A CoCl2·6H2O solution (solute 1.7845 g, deionized water 7.5 mL) and a NaOH solution (solute 0.3 g, deionized water 7.5 mL) were sequentially added to a Co(NO3)2·6H2O solution (solute 4.3655 g, deionized water 15 mL), stirred for 30 min, then transferred to a 50 mL polytetrafluoroethylene lined reaction kettle, and hydrothermally reacted at 180°C for 5 h, naturally cooled to room temperature, then centrifuged to obtain a precipitate, which was washed with deionized water to remove residual ions, vacuum dried at 60°C for 8 h, placed in a muffle furnace, heated to 350°C at a heating rate of 3°C, and calcined for 2 h to obtain Co3O4 nanocubes; (3) The CuWO4 nanoparticles prepared in step (1) and the Co3O4 nanocubes prepared in step (2) are mixed (Cu:Co molar ratio 1:0.1), dispersed in 30 mL of ethanol, ultrasonically treated for 30 min, then stirred at 60°C until the ethanol is completely evaporated, to obtain a precursor powder, and then heated at a rate of 5°C to 180°C and calcined for 2 h, to obtain a CuWO4@Co3O4 composite material (CuWO4@Co3O4-10%).

[0059] Example 2: A CuWO4@Co3O4 composite material, the preparation method comprising the following steps: In step (3), the Cu:Co molar ratio is 1:0.3, to obtain a CuWO4@Co3O4 composite material (CuWO4@Co3O4-30%), and the rest is the same as in Example 1.

[0060] Example 3: A CuWO4@Co3O4 composite material, the preparation method comprising the following steps: In step (3), the Cu:Co molar ratio is 1:0.5, to obtain a CuWO4@Co3O4 composite material (CuWO4@Co3O4-50%), and the rest is the same as in Example 1.

[0061] Example 4: A CuWO4@Co3O4 composite material, the preparation method comprising the following steps: In step (3), the Cu:Co molar ratio is 1:0.7, to obtain a CuWO4@Co3O4 composite material (CuWO4@Co3O4-70%), and the rest is the same as in Example 1.

[0062] Example 5: A CuWO4@Co3O4 composite material, the preparation method comprising the following steps: In step (3), the Cu:Co molar ratio is 1:1, to obtain a CuWO4@Co3O4 composite material (CuWO4@Co3O4-100%), and the rest is the same as in Example 1.

[0063] Example 6: A CuWO4@Co3O4 composite material, the preparation method comprising the following steps: (1) NaWO4·2H2O solution (solute 0.25 g, deionized water 15 mL) was dropped into Cu(NO3)2·3H2O solution (solute 0.2 g, deionized water 15 mL), continuously stirred at room temperature for 20 min, then transferred to a 50 mL polytetrafluoroethylene lined reaction kettle, hydrothermal reaction at 150℃ for 30 h, naturally cooled to room temperature, then centrifuged at 8000 rpm to obtain the precipitate, which was washed with deionized water and ethanol in sequence to remove impurities, and placed in a muffle furnace, heated to 400℃ at a rate of 4℃, and calcined for 3 h to obtain CuWO4 nanoparticles; (2) CoCl2·6H2O solution (solute 1 g, deionized water 7 mL) and NaOH solution (solute 0.2 g, deionized water 7 mL) were sequentially added to Co(NO3)2·6H2O solution (solute 4 g, deionized water 12 mL), stirred for 20 min, then transferred to a 50 mL polytetrafluoroethylene lined reaction kettle, hydrothermal reaction at 150℃ for 10 h, naturally cooled to room temperature, then centrifuged to obtain the precipitate, which was washed with deionized water to remove residual ions, vacuum dried at 50℃ for 10 h, placed in a muffle furnace, heated to 300℃ at a rate of 2℃, and calcined for 3 h to obtain Co3O4 nanocubes; (3) The CuWO4 nanoparticles prepared in step (1) and the Co3O4 nanocubes prepared in step (2) were mixed (Cu to Co molar ratio 1:0.1), dispersed in 30 mL of ethanol, and ultrasonically treated for 30 min, then stirred at 40℃ until the ethanol was completely evaporated, to obtain a precursor powder, which was then calcined at 150℃ at a rate of 4℃ for 3 h to obtain CuWO4@Co3O4 composite material.

[0064] Example 7: A CuWO4@Co3O4 composite material, the preparation method comprising the following steps: (1) NaWO4·2H2O solution (solute 0.35 g, deionized water 15 mL) was dropped into Cu(NO3)2·3H2O solution (solute 0.3 g, deionized water 15 mL), continuously stirred at room temperature for 40 min, then transferred to a 50 mL polytetrafluoroethylene lined reaction kettle, hydrothermal reaction at 200℃ for 20 h, naturally cooled to room temperature, then centrifuged at 8000 rpm to obtain the precipitate, which was washed with deionized water and ethanol in sequence to remove impurities, and placed in a muffle furnace, heated to 600℃ at a rate of 6℃, and calcined for 1 h to obtain CuWO4 nanoparticles; (2) CoCl2·6H2O solution (2g solute, 8mL deionized water) and NaOH solution (0.5g solute, 8mL deionized water) were added sequentially to Co(NO3)2·6H2O solution (5g solute, 18mL deionized water), stirred for 40min, and then transferred to a 50mL polytetrafluoroethylene-lined reactor. The reactor was hydrothermally reacted at 200℃ for 8h, cooled naturally to room temperature, and then centrifuged to obtain the precipitate. The precipitate was washed with deionized water to remove residual ions, dried under vacuum at 70℃ for 5h, placed in a muffle furnace, heated to 400℃ at a heating rate of 4℃, and calcined for 1h to obtain Co3O4 nanocubes. (3) The CuWO4 nanoparticles obtained in step (1) and the Co3O4 nanocubes obtained in step (2) were mixed (Cu to Co molar ratio 1:0.1), dispersed in 30 mL of ethanol, ultrasonically treated for 30 min, and then stirred at 80 °C until the ethanol was completely evaporated to obtain precursor powder. The temperature was then increased to 200 °C at a heating rate of 6 °C and calcined for 1 h to obtain CuWO4@Co3O4 composite material.

[0065] Experimental Example 1: XRD Analysis X-ray diffraction analysis was performed on the CuWO4 nanoparticles, Co3O4 nanocubes, and CuWO4@Co3O4 composite material (CuWO4@Co3O4-70%) prepared in Example 4. The samples were analyzed using a Panaco X'Pert PRO X-ray diffractometer at a scanning speed of 10° / min and a scanning angle of 10-70°. The results are shown below. Figure 1 .

[0066] Depend on Figure 1 It can be seen that the main peaks of CuWO4 at 2θ=23.6°, 24.3°, 30.1°, and 36.2° perfectly match those of the standard card PDF#43-1003, confirming its high crystallinity.

[0067] The characteristic peaks of Co3O4 at 2θ = 19.0°, 31.3°, 36.9°, 59.4°, and 65.2° correspond to a spinel structure (PDF#21-0307), indicating that its {111}, {220}, and {311} crystal planes are preferentially grown.

[0068] For the CuWO4@Co3O4 composite material, its diffraction peaks are composed of the superposition of characteristic peaks of CuWO4 and Co3O4. For example, the (-112) crystal plane of CuWO4 at 36.2° and the (311) crystal plane of Co3O4 at 36.9° coexist, and no impurity peaks appear, which confirms that the two phases still maintain the integrity of their respective crystal structures after being combined.

[0069] CuWO4@Co3O4 composite material has all the peaks of the two corresponding substances, indicating the successful preparation of the material.

[0070] Test Example 2: UV-Vis diffuse reflectance analysis CuWO4@Co3O4-10%, CuWO4@Co3O4-30%, CuWO4@Co3O4-50%, CuWO4@Co3O4-70% and CuWO4@Co3O4-100% prepared in Example 4, Co3O4, and Example 1-5 were characterized. The UV-Vis diffuse reflectance spectra of the above samples were obtained using an Agilent Cary 100 type UV spectrophotometer with barium sulfate as a reference under the condition of a spectral range of 200-800 nm. The results are shown in Figures 2-3 .

[0071] As can be seen from Figure 2 , Co3O4 has the highest light absorption in the wavelength range of 350-800 nm, and CuWO4 has a light absorption range of 350-510 nm, but the light absorption intensity is lower. With the increase of the composite ratio of Co3O4, the absorption intensity of the composite material in the range of 350-800 nm is improved. The light absorption intensity of CuWO4@Co3O4-50% in the range of 350-500 nm is higher than that of CuWO4@Co3O4-70%, which indicates that CuWO4@Co3O4-50% has strong visible light absorption. The absorption intensity of CuWO4@Co3O4-70% in the range of 600-800 nm is higher, which indicates that CuWO4@Co3O4-70% has strong infrared light absorption and can better utilize the photothermal capacity of infrared light.

[0072] As can be seen from Figure 3 , the band gap of Co3O4 and CuWO4 is 1.21 eV and 2.37 eV, respectively. When CuWO4 is combined with Co3O4, the band gap of the composite material CuWO4@Co3O4-70% is narrowed to different degrees, and the band gap is 1.82 eV. This indicates that after the combination of the two materials, a heterojunction is formed, which enhances the light absorption performance and widens the light absorption range. Under irradiation, it is possible to generate more photo-generated carriers, which is conducive to the photoexcitation of valence band electrons to the conduction band, so as to participate in the subsequent NO x - reduction reaction.

[0073] Test Example 3: Adsorption isotherm and specific surface area and pore size distribution analysis The adsorption isotherms, specific surface area, and pore size distribution of CuWO4, Co3O4, and CuWO4@Co3O4-70% prepared in Example 4 were analyzed using a Micromeritics ASAP 2460 instrument. The results are shown in [Figure number missing]. Figures 4-6 .

[0074] Depend on Figure 4 According to the nitrogen adsorption-desorption curve analysis, CuWO4 material exhibits typical type IV isotherm characteristics: the steep rise and significant hysteresis loop in the high-pressure region (P / P0>0.8) indicate that the material has a highly ordered mesoporous structure (presumably type H1 hysteresis loop) and regular pore arrangement.

[0075] Depend on Figure 5 It can be seen that the adsorption curve of Co3O4 material rises gently in the low-pressure region, the slope increases in the medium-pressure region (P / P0 = 0.4-0.8), and rises sharply in the high-pressure region (P / P0>0.8) and forms a significant hysteresis loop, confirming the mesoporous capillary condensation effect. The desorption curve closes steeply at P / P0 ≈0.8, which is consistent with the H2 type hysteresis loop, and is speculated to be due to ink bottle-shaped channels or complex channel connectivity.

[0076] Depend on Figure 6 It can be seen that the CuWO4@Co3O4-70% material exhibits a V-shaped isotherm, which is a typical characteristic of mesoporous materials. In the low-pressure region (P / P0<0.1), the slope rises gently with fewer micropores; in the medium-pressure region (P / P0 = 0.4-0.8), the slope increases, mainly due to the formation of multilayer adsorption; in the high-pressure region (P / P0>0.9), the slope rises sharply and a wide hysteresis loop appears, with the hysteresis loop closure point located at P / P0 ≈ 0.5, consistent with the H3 type.

[0077] The pore size distribution maps obtained using the Barrett-Joyner-Halenda (BJH) method show that the average pore sizes of CuWO4, Co3O4, and CuWO4@Co3O4-70% are 56.81, 19.60, and 28.75 nm, respectively, indicating that the channels of CuWO4, Co3O4, and CuWO4@Co3O4-70% are predominantly mesoporous. The specific surface areas of CuWO4, Co3O4, and CuWO4@Co3O4-70% calculated using the Brunauer-Emmett-Teller (BET) method are 6.74, 6.67, and 7.9712 m², respectively. 2 g -1 The composite of CuWO4 and Co3O4 increases the specific surface area of ​​CuWO4@Co3O4 by 70%. A larger specific surface area increases the number of reactive sites, which is beneficial for NO reactivity. x - Adsorption and reaction.

[0078] Test Example 4: Light response performance determination The linear sweep voltammograms of CuWO4, Co3O4, CuWO4@Co3O4-70% composite electrodes prepared in Example 4 were tested by an electrochemical workstation of model CHI6503, using a three-electrode system, with an Ag / AgCl electrode as the reference electrode, a platinum electrode as the counter electrode, and the sample under test as the working electrode. The results are shown in Figure 7 .

[0079] As can be seen from Figure 7 , the current densities of CuWO4, Co3O4, and CuWO4@Co3O4-70% at -0.5 V vs. RHE were -7.483, -10.04, and -18.14 mA·cm -2 , respectively. The photocurrent of CuWO4@Co3O4-70% was 2.42 and 1.81 times that of pure CuWO4 and pure Co3O4, respectively.

[0080] Test Example 5: Photosensitivity determination The photosensitivity of CuWO4, Co3O4, and CuWO4@Co3O4-70% composite electrodes prepared in Example 4 was determined by an electrochemical workstation of model CHI6503, and the I-t curves were determined. The results are shown in Figure 8 .

[0081] As can be seen from Figure 8 , the photocatalytic material CuWO4@Co3O4-70% had the highest photocurrent response in the current density at the moment of turning on and off the light, and the photocurrent was stable in repeated 10 times of turning on and off the light. The photocurrent response of CuWO4 was lower than that of CuWO4@Co3O4-70%, and Co3O4 had almost no photocurrent response. This confirmed that the photocurrent of CuWO4@Co3O4-70% prepared by compounding pure CuWO4 and pure Co3O4 was significantly enhanced, and the utilization efficiency of photocurrent was significantly improved by the construction of heterojunction.

[0082] Test Example 6: Electrochemical impedance spectrogram determination The electrochemical impedance spectrograms of CuWO4, Co3O4, and CuWO4@Co3O4-70% prepared in Example 4 were determined to test the carrier migration and separation kinetics of the electrodes. Generally, the smaller the electrochemical impedance spectrogram radius, the greater the photoelectron-hole transfer rate. The results are shown in Figure 9 .

[0083] As can be seen from Figure 9 , the radius of CuWO4 was the largest, and the electrochemical impedance spectrogram radius of CuWO4@Co3O4-70% became smaller after compounding Co3O4, indicating that the construction of CuWO4 and Co3O4 heterojunction increased the reaction kinetics and improved the carrier transport efficiency.

[0084] Experimental Example 7: Photocatalytic Activity Determination This study utilizes tip discharge plasma activation of air, where high-energy electrons bombard nitrogen and oxygen to generate active intermediates. The nitrogen oxides formed by the interaction of these active intermediates are fixed into NO⁻ and NO⁻ in a 1 mol / L KOH alkaline electrolyte. The photoelectrocatalytic ammonia synthesis performance of the samples was investigated using an electrolyte solution activated by plasma for half an hour. CuWO₄ and Co₃O₄ prepared in Example 4, and CuWO₄@Co₃O₄-10%, CuWO₄@Co₃O₄-30%, CuWO₄@Co₃O₄-50%, CuWO₄@Co₃O₄-70%, and CuWO₄@Co₃O₄-100% prepared in Examples 1-5 were then subjected to constant potential electrolysis (NO₃O₄ is generated at the cathode). x - The reduction reaction and hydrogen evolution reaction (oxygen evolution reaction occurs at the anode) were carried out over a period of 2 hours with a stirring speed of 200 rpm. Samples were taken after 2 hours of reaction to determine the yield. Results are shown below. Figure 10 .

[0085] Depend on Figure 10 It can be seen that, at a bias voltage of -0.5 V vs. RHE, the ammonia yields of CuWO4 and Co3O4 prepared in Example 4, and CuWO4@Co3O4-10%, CuWO4@Co3O4-30%, CuWO4@Co3O4-50%, CuWO4@Co3O4-70%, and CuWO4@Co3O4-100% prepared in Examples 1-5 were 119.2, 157.2, 210, 217.9, 225.6, 267.2, and 179 mmol·h⁻¹, respectively. -1 ·g cat -1 The Faraday efficiencies were 79.3%, 81.2%, 67.9%, 82.5%, 88.2%, 89.7%, and 63.9%. The ammonia synthesis efficiency of CuWO4@Co3O4-70% was 2.24 times and 1.7 times that of CuWO4 and Co3O4, respectively. The heterojunction formed by CuWO4 and Co3O4 modulates the carrier transport channel, which is beneficial to electron-hole separation and significantly improves the ammonia synthesis efficiency.

[0086] Experimental Example 8: Stability Determination The CuWO4@Co3O4-70% prepared in Example 4 was subjected to a stability test, and six cycles of ammonia synthesis were conducted under the same conditions as in Example 7. The results are shown below. Figure 11 .

[0087] Depend on Figure 11It can be known that after 6 cycles of the 2 h plasma coupling photoelectrocatalytic reduction synthesis of ammonia reaction under a bias voltage of-0.5 V vs.RHE, the ammonia yield of the catalyst is kept at a stability of 97%.

[0088] In conclusion, the CuWO4 is successfully compounded with Co3O4, and according to the Cu / Co atomic molar ratio, the CuWO4@Co3O4-x composite catalyst with higher photoelectrocatalytic nitrogen reduction synthesis of ammonia performance is prepared, the construction of heterojunction reduces the valence band position of CuWO4@Co3O4-x, reduces the free energy of the electron transition from Co3O4 to CuWO4, and is beneficial to accelerate the electron transfer, thereby further promoting the NO x - Reduction reaction CuWO4@Co3O4-x has stronger NO x - adsorption effect, which provides a good foundation for the activation of the subsequent N=O double bond and the subsequent hydrogenation reduction step of the intermediate; at the same time, the construction of heterojunction reduces the recombination of photoinduced electrons and holes, accelerates the charge transfer, and significantly improves the synthesis of ammonia efficiency.

[0089] The above only describes the preferred embodiments of the present application and is not used to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing CuWO4@Co3O4 composite material, characterized in that, The method comprises the following steps: (1) adding NaWO4·2H2O solution into Cu(NO3)2·3H2O solution, stirring, then reacting, cooling to room temperature, and separating and calcining to prepare CuWO4 nanoparticles; (2) adding CoCl2·6H2O solution and NaOH solution into Co(NO3)2·6H2O solution in sequence, stirring, then reacting, cooling to room temperature, and separating, drying and calcining to prepare Co3O4 nanocubes; (3) mixing CuWO4 nanoparticles prepared in step (1) and Co3O4 nanocubes prepared in step (2), dispersing in ethanol, ultrasonicating, then stirring, and calcining to prepare CuWO4@Co3O4 composite material.

2. The method for preparing CuWO4@Co3O4 composite material according to claim 1, characterized in that, In step (1), the volume ratio of NaWO4·2H2O solution to Cu(NO3)2·3H2O solution is 0.8-1.2:0.8-1.

2.

3. The method for preparing CuWO4@Co3O4 composite material according to claim 1, characterized in that, In step (1), the reaction is carried out at 150-200℃ for 20-30h.

4. The method for preparing CuWO4@Co3O4 composite material according to claim 1, characterized in that, In step (1), the calcining is carried out at 400-600℃ for 1-3h. 5.The method of claim 1, wherein the CuWO 4 @ Co 3 O 4 composite material is prepared by the steps of, In step (2), the volume ratio of CoCl2·6H2O solution, NaOH solution and Co(NO3)2·6H2O solution is 7-8:7-8:12-18. 6.The method of claim 1, wherein the CuWO 4 @Co 3 O 4 composite material is prepared by the steps of, In step (2), the reaction is carried out at 150-200℃ for 5-10h. 7.The method of claim 1, wherein the CuWO 4 @ Co 3 O 4 composite material is prepared by the steps of, In step (2), the calcining is carried out at 300-400℃ for 1-3h. 8.The method of claim 1, wherein the CuWO 4 @Co 3 O 4 composite material is prepared by the steps of, In step (3), the molar volume ratio of Cu atoms in CuWO4 nanoparticles, Co atoms in Co3O4 nanocubes and ethanol is 1mol:0.1-1mol:30mL.

9. CuWO4@Co3O4 composite material prepared by the method of any one of claims 1-8.

10. Application of CuWO4@Co3O4 composite material of claim 9 in plasma-coupled photoelectrocatalytic synthesis of ammonia.

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